The present invention relates to spinal implant device, and more particularly to spinal cages useful in laminoplasty surgery.
Spinal stenosis is the narrowing of the spinal cord canal, and can result in pain, weakness in arms and/or legs, and unsteadiness in the gait. For mild conditions, conservative treatment may be sufficient. When symptoms are severe or progressive, however, cervical laminoplasty surgery may be required to enlarge the spinal canal to relieve compression of the spinal cord. Common indications which give rise to a need for laminoplasty surgery include stenosis of the spinal canal, ossification of the posterior longitudinal ligament (OPLL), and spondylotic myelopathy.
Surgical techniques used to perform laminoplasty surgery can vary and will depend on many factors, including the source of the spinal cord compression, the number of vertebral segments involved in the disease process, and the cervical alignment. Two common surgical laminoplasty techniques include open door laminoplasty and midline splitting laminoplasty. In open door laminoplasty, the lamina is cut on one side and hinged on the other side. The lamina is then rotated to open the canal, and sutures are placed on the hinged side to maintain the opening. Eventually, bone growth will fill in the gap created on the cut side. In midline splitting laminoplasty, both sides of the lamina are hinged, and the spinous process is bisected into two halves. Both halves are then rotated outwards, and a strut graft is placed between the halves to secure the opening.
Several devices exists for maintaining or stabilizing the lamina in the open or split position. U.S. Pat. No. 6,080,157 of Cathro et al., for example, discloses a device for stabilizing the lamina after open door laminoplasty surgery. The device includes a spacer which is shaped to engage between severed edges of a lamina, and a retainer attached to the spacer which is adapted to maintain the spacer in an operative position. U.S. Pat. No. 6,358,254 of Anderson also discloses a device for expanding the spinal canal. The device includes two stents, two washers, two screws, and a cable. In use, pedicle cuts are made in the vertebra, and a screw is then inserted into each cut, through a washer and a stent, to expand the cut bone. The cable is then attached to each washer and strapped around the posterior portion of the vertebrae to stabilize the expanded canal and allow the vertebrae to heal with the spinal canal expanded.
While these devices have proven effective, they can be difficult to implant, resulting in increased medical costs. Moreover, the devices do not have a substantially low-profile, and thus can potentially cause damage to surrounding tissue and/or to the spinal cord. The devices are also not designed to restore the natural dynamics of the cervical spine, and thus can cause discomfort to the patient.
Accordingly, there exists a need for an improved laminoplasty implant that is effective to maintain and stabilize the position of the lamina after laminoplasty surgery. Moreover, there is a need for a device that can be easily and safely implanted, that will allow for permanent bony incorporation when used with bone growth promoting materials, that will allow for muscle re-attachment, and that will restore the natural dynamics of the cervical spine.
The present invention provides a medical implant device having a hollow elongate body including a longitudinal axis, opposed cephalad and caudal sides, and opposed posterior and anterior sides adjacent to the cephalad and caudal sides. The cephalad, caudal, posterior, and anterior sides define an inner lumen having opposed first and second open ends. The implant can be used for a variety of applications, but is preferably used to stabilize and maintain the position of a bisected spinous process after laminoplasty surgery.
In one embodiment, at least one of the cephalad side, the caudal side, and the posterior side includes at least one perforation formed therein, and the anterior side of the body is perforation-free. Preferably, the cephalad side, the caudal side, and the posterior side each include a several perforations formed therein. The perforations can have a variety of shapes and size, but are preferably elongated slots extending in a direction transverse to the longitudinal axis of the of the elongate body. The slots can optionally include a suture-receiving recess formed therein for retaining suture.
In another embodiment, the anterior side of the implant includes a first edge mated to the cephalad side and a second edge mated to the caudal side. Preferably, the first and second edges of the anterior side are substantially rounded. The anterior side of the elongate body can also be curved along the longitudinal axis such that an outer surface of the anterior side is concave. The rounded edges and the curved anterior side prevent potential abrasion or damage to tissue surrounding the implant, and provide additional space for the spinal cord in the spinal canal. The entire elongate body can also be curved along the longitudinal axis such that an outer surface of the anterior side is concave, and an outer surface of the posterior side is convex. That is, the planes defined by the first and second open ends are converging. This can be effected by designing the elongate body with the posterior side being longer than the anterior side.
In another embodiment, the elongate body preferably has an anatomical cross-section extending in a direction transverse to the longitudinal axis, such that the cross-section of the elongate body conforms to the shape of a patient""s bisected spinous process. By way of non-limiting example, the cross-section can be in the shape of a parallelogram, a square, a rectangle, a diamond, an oval, and a circle. The first and second open ends of the elongate body can also have an anatomical shape such that they are adapted to be positioned between a split spinous process of a patient""s spinal system. Preferably, the first and second open ends are angled with respect to the longitudinal axis.
In another embodiment, the elongate body includes first and second halves positioned on opposed sides of a midpoint of the body. The first and second halves are preferably angled with respect to one another, such that the implant is bent at the midpoint. The bend is effective to provide additional space for the spinal cord within the spinal canal.
In other aspects of the invention, the implant can include a spinous process replacement member extending outward from the body in a direction transverse to the longitudinal axis. In another embodiment, the implant can include at least one radiopaque member disposed therein and configured to provide an x-ray visible reference to indicate the position of the implant with respect to an anatomical structure when the implant is positioned within an interstitial space.
In yet another embodiment of the present invention, a medical implant device is provided having a hollow elongate body including a longitudinal axis, opposed cephalad and caudal sides, and opposed posterior and anterior sides adjacent to the cephalad and caudal sides. The cephalad side, caudal side, posterior side, and anterior side define an inner lumen having opposed first and second open ends. The implant further includes a fixation element receiving member mated to the posterior side of the implant, adjacent the first open end. The fixation element receiving member extends at an angle with respect to the longitudinal axis and is effective to receive a fixation element for attaching the implant to a bone structure.
In other aspects, the posterior and anterior sides of the implant have a length extending along the longitudinal axis greater than a length of the cephalad and caudal sides, and the cephalad and caudal sides each include a concave recess formed adjacent each of the first and second ends, such that the first and second ends are adapted to seat a bone structure. The anterior side of the implant, adjacent the first open end, can also include an extension member opposed to the fixation element receiving member.